Clinical implications of scalp ictal EEG pattern in patients with temporal lobe epilepsy

ObjectiveTo determine the clinical implications of scalp ictal EEG pattern in patients with temporal lobe epilepsy (TLE).MethodsScalp EEG ictal patterns were retrospectively determined in 27 consecutive patients with medically refractory temporal lobe epilepsy who underwent phase-1 scalp video-EEG and phase-2 simultaneous scalp and intracranial video-EEG recordings for pre-surgical evaluation.ResultsOf the 192 temporal lobe seizures recorded during phase-1 and phase-2 scalp video-EEG studies, 124 (65%) seizures were associated with theta/alpha (5–9 Hz) ictal onset pattern, and 68 (35%) seizures were associated with delta (2–5 Hz) ictal onset pattern. Fourteen (52%) patients had exclusively theta/alpha ictal onset, 3 (11%) patients had exclusively delta ictal onset, and 10 (37%) patients had mixed theta/alpha and delta ictal onsets. MTLE was observed in 26 patients who had 124 seizures with theta/alpha ictal onset and 59 seizures with delta ictal onset. LTLE was observed in one patient who had 9 seizures with delta ictal onset. Scalp ictal EEG pattern was not significantly correlated with postsurgical seizure outcomes.ConclusionsBoth scalp delta and theta/alpha ictal onset patterns can be commonly found in patients with MTLE.SignificanceScalp delta ictal onset is not a unique EEG pattern for LTLE as commonly believed.     

颅内电极监测对顽固性颞叶癫痫致痫灶的定位价值

目的:探讨发作期及发作间期颅内电极监测对癫痫灶的定位作用。方法:20例难治性颞叶癫痫,经临床、影像学及头皮脑电图不能确定致痫灶部位,应用立体定向技术,在患者双侧颞叶植入硬膜下条状电极,进行长时间视频脑电图监测,记录发作期和发作间期的脑电图变化,并与头皮脑电图、MRI进行比较,分析癫痫灶部位,进行手术治疗,术后跟踪随访,评估致痫灶定位的准确性。结果:20例癫痫病人颅内电极埋藏时间1～5天,每个患者至少监测到2次临床发作,每一病例均记录发作间期和发作期的异常放电活动。15例发作间期与发作期定侧一致,2例发作间期为双侧棘波病灶,3例发作间期定位与发作期不一致。按Engel术后效果分级:手术效果满意(癫痫发作消失)13例(65%),显著改善3例(15%),良好3例(15%),无效1例(5%)。所有病例均未出现因颅内电极埋藏而致的并发症。结论:对于致痫灶不能定位的难治性癫痫,应用颅内电极记录方法,尤其是发作期起始时脑电图变化,可以确定致痫灶位置,为癫痫手术治疗提供可靠的依据。     

Interictal EEG and ictal scalp EEG propagation are highly predictive of surgical outcome in mesial temporal lobe epilepsy

PURPOSE: Surgical outcome in patients with mesial temporal lobe sclerosis (MTS) is worse than that in patients with temporal lobe activity (TLE) with tumors. Previous studies of the ictal EEG focused on ictal EEG onset in scalp EEG or ictal EEG propagation in invasive recordings. Ictal EEG propagation with scalp electrodes has not been reported. METHODS: Ictal scalp EEG propagation patterns were studied in 347 seizures of 58 patients with MTS or nonlesional TLE. Interictal epileptiform discharges (IEDs) and the presence of unilateral mesial temporal lobe atrophy in magnetic resonance imaging (MRI) also were studied in these 58 patients. Forty-nine patients were operated on (minimal follow-up of 1 year). RESULTS: Postoperatively, seizure-free outcome was seen in (a) 82.8% of patients with regionalized EEG seizure without contralateral propagation, but in only 45.5% of patients with contralateral propagation (p = 0.007); (b) 84.6% of patients with 100% IED lateralized to one temporal lobe, but in only 52.2% with <100% unitemporal IED (p = 0.015); (c) 88.9% with 100% unitemporal IED and regionalized ictal EEG combined, 73.7% with one of both variables, and only 33.3% with <100% ipsitemporal IED combined with contralateral ictal EEG propagation (p = 0.007). CONCLUSIONS: Switch of lateralization or bitemporal asynchrony in the ictal scalp EEG and bitemporal IED are most probably an index of bitemporal epileptogenicity in MTS and are associated with a worse outcome.     

High-frequency oscillations of ictal muscle activity and epileptogenic discharges on intracranial EEG in a temporal lobe epilepsy patient.

OBJECTIVE: During seizures, intracranial EEG electrodes can record ictal muscle movements. Our purpose was to differentiate the high-frequency oscillations (HFOs) of extracranial muscle contractions from those of intracranial epileptogenic discharges. METHODS: Using intracranial video-EEG (IVEEG), we recorded seizures in a 17-year-old boy with left mesial-temporal lobe epilepsy. We used multiple band frequency analysis (MBFA) to differentiate extracranial HFOs of craniofacial muscle activities from intracranial HFOs recorded ictally and interictally. RESULTS: During 11 seizures, IVEEG showed low-amplitude fast waves ( approximately 60Hz) starting at the left mesial-temporal electrodes. Ictal facial grimacing projected low-amplitude ( approximately 20muV) fast waves ( approximately 160Hz) on inferior lateral-temporal electrodes. Interictal chewing projected medium-amplitude ( approximately 100muV) fast waves ( approximately 140Hz) correlating to mouth movements. MBFA topographic power spectrograms revealed a sustained, consistent ictal fast-frequency band from electrodes in the seizure-onset zone and randomly scattered HFOs without a specific frequency band from ictal and interictal extracranial muscle contractions. CONCLUSIONS: MBFA power spectrograms differentiated randomly scattered muscle HFOs without a specific frequency band at electrodes close to temporal muscles from ictal epileptic HFOs with a sustained, fast-frequency band in the seizure-onset zone. SIGNIFICANCE: The pattern and distribution of frequency power spectrograms of extracranial HFOs differ from those of intracranial HFOs.     

Lateralization of the epileptogenic focus in temporal lobe epilepsy by scalp P300

The P300 is a cognitive event-related potential partially generated by the amygdala/hippocampus complex, the most common source of temporal lobe epilepsy (TLE). In order to test the hypothesis that scalp P300 amplitude is reduced ipsilateral to the epileptogenic focus in TLE, we performed a prospective study of 15 subjects with TLE and compared the lateralizing ability of scalp P300 to interictal EEG. P300 asymmetries in TLE were compared with asymmetries in a control group. P300 amplitude was significantly attenuated ipsilateral to the epileptic focus. P300 amplitude reduction correctly lateralized the focus in 82% of the cases (p = 0.02). We conclude that scalp P300 accurately lateralizes the epileptogenic focus in TLE. Further studies are needed to define the potential role of P300 in the presurgical evaluation of TLE.     

Independent component analysis of ictal EEG in medial temporal lobe epilepsy

PURPOSE: Application of independent component analysis (ICA) to interictal EEGs and to event-related potentials has helped noise reduction and source localization. However, ICA has not been used for the analysis of ictal EEGs in partial seizures. In this study, we applied ICA to the ictal EEGs of patients with medial temporal lobe epilepsy (TLE) and investigated whether ictal components can be separated and whether they indicate correct lateralization. METHODS: Twenty-four EEGs from medial TLE patients were analyzed with the extended ICA algorithm. Among the resultant 20 components in each EEG, we selected components with an ictal nature and reviewed their corresponding topographic maps for the lateralization. We then applied quantitative methods for the verification of increased quality of the reconstructed EEGs. RESULTS: All ictal EEGs were successfully decomposed into one or more ictal components and nonictal components. After EEG reconstruction with exclusion of artifacts, the lateralizing power of the ictal EEG was increased from 75 to 96%. CONCLUSIONS: ICA can separate successfully the manifold components of ictal rhythms and can improve EEG quality.     

Automatic lateralization of temporal lobe epilepsy based on scalp EEG.

OBJECTIVE: The objective of this work is the determination of the lateralization of the epileptic seizure onset zone using the scalp EEG signal processing. METHODS: A comprehensive method based on the evaluation of the evolution of the correlation coefficients computed between bipolar channels (longitudinal montage) was applied to 43 patients (87 seizures). The correlation coefficients are estimated by a nonlinear regression analysis. The methodology that leads to the lateralization is based on several processing steps: segmentation, seizure onset determination and then lateralization. RESULTS: Results show that the mean level of the nonlinear correlation values computed between EEG channels at the seizure onset time is significantly higher on the side of the beginning of a seizure. CONCLUSIONS: The side of the seizure onset was determined for about 80-90% of the seizures studied with a satisfactory high reproducibility level. SIGNIFICANCE: Comparison of nonlinear correlation coefficients between both sides of the brain leads to the determination of the side of seizure onset.     

Ictal scalp EEG findings in patients with mesial temporal lobe epilepsy.

The syndrome of mesial temporal lobe epilepsy (MTLE) is a well-defined clinical entity that responds to surgical treatment in a considerable number of patients. Although it has been subjected to intensive clinical research, few investigators have published the ictal scalp EEG findings and looked for specific features that might predict postoperative outcome. This study was designed to examine ictal scalp EEG characteristics in detail, in a group of patients with pathologically confirmed hippocampal sclerosis (HS). Patients who underwent long-term video-EEG monitoring at our center during a 3-year period and were diagnosed to have MTLE and pathologically proven HS were included in this retrospective study. All ictal scalp EEGs were investigated in a common reference montage, paying attention to the localization, morphology and frequency of ictal discharges that were accepted to represent a specific phase if the findings were sustained for at least 3 seconds. Any significant change in localization, morphology or frequency of discharges was said to represent a different phase. The ictal EEG patterns in different phases were later compared among seizures of different patients. In addition, the ictal EEG characteristics of the patients in Group I (Engel's classification) were compared with the ictal EEG findings in patients who were included in another group. All the patients have been followed for more than 5 years. Seventy-one ictal EEGs were investigated in 25 adult patients (11 M, 14 F). Onset patterns were lateralized in 81.7% and localized in 76% of the seizures. Thirteen different patterns of onset were detected, the most common of which was the cessation of interictal discharges (35.2%). The most common ictal pattern following the initial changes was ipsilateral temporal rhythmic theta-delta activity (85.2%) that occurred on the average 13.4 seconds after onset. Nonlocalized/lateralized seizure onset of all the seizures or bilateral independent onset was present in 75% of the patients in Groups II-III, whereas this ratio was 14.3% in the patients in Group I (p=0.031). In conclusion, ictal scalp EEG in MTLE allows correct lateralization and localization in most of the seizures. Onset patterns may vary considerably; however, a later significant pattern consisting of rhythmic ipsilateral temporal build-up develops in the majority of seizures. Some ictal EEG characteristics may be related to post-operative outcome.     

Intracranial localisation of ictal urinary urge epileptogenic zone to the non-dominant temporal lobe

Ictal urinary urge is a rare symptom of focal epilepsy usually localising to the non-dominant hemisphere, specifically, the temporal lobe. Lateralisation in previously described cases has been established using scalp video-EEG monitoring or functional imaging. We report the case of a 19-year-old girl with refractory epilepsy and ictal urinary urge arising from the non-dominant temporal lobe, confirmed by invasive, subdural EEG monitoring. Since undergoing a temporal lobectomy two and a half years ago, the patient has not experienced ictal urinary urge. To our knowledge, this is the first report demonstrating localisation of ictal urinary urge epileptogenic zone to the non-dominant temporal lobe by invasive intracranial monitoring.     

颞叶癫痫发作初期头皮和颅内脑电定位价值的比较研究

目的 比较研究颞叶癫痫发作初期头皮脑电(sEEG)和颅内脑电(iEEG)的特点,探讨有定位意义的EEG指标.方法 常规行长程视频EEG(Video-EEG,V-EEG)监测,以捕捉到3次以上发作为标准.对sEEG难以定位的患者采用颅内埋置硬膜下和(或)深部电极,记录iEEG.结果 本组20例资料显示,sEEG和iEEG的定位检出率分别为50%和100%.经iEEG记录分析,7例sEEG不能定侧者5例完成定侧,10例广泛性sEEG异常者均定位为区域性或局限性表现.结论 低幅快节律、棘波和尖波节律具有重要的的定位价值;80%的sEEG低幅快节律表现者,与iEEG监测中表现一致;80%的sEEG颞叶棘波表现者,在iEEG监测中存在尖波节律.iEEG能明显提高致痫灶的定侧和定位准确性.     

Two types of remote propagation in mesial temporal epilepsy: analysis with scalp ictal EEG.

The purpose of this study was to describe the propagation pattern of ictal discharges, particularly remote patterns from a localized onset in patients with mesial temporal epilepsy, and to determine whether this provides additional information to that obtained from prolonged presurgery scalp EEG monitoring. This is a retrospective and analytical study that included a historical open cohort of 18 patients with mesial temporal epilepsy, among whom 56 regionalized-lateralized onset seizures were recorded. These seizures were analyzed as to whether remote propagation occurred and as to their temporal characteristics. Thirty-eight regionalized-lateralized onset seizures did not show remote propagation, whereas 18 did. Two types of remote propagation were identified, one early and one late, depending on whether the remote propagation occurred before or after 10 seconds had elapsed from the onset of the electroencephalographic seizure. When the seizures were compared according to the type of propagation, those with early remote propagation showed a correlation, not statistically significant, with the intractability of the epilepsy (P = 0.0754), toward independent bitemporal interictal discharges (P = 0.1667), and from the MRI perspective, to occur with temporal lesions other than pure mesial sclerosis (P = 0.6329). Early remote propagation seizures were not associated with nonlateralized onset (P = 0.2682). The only patient in our study with switch of lateralization seizures experienced early remote propagation seizures. Patients with late remote propagation seizures and those without remote propagation showed no statistically significant differences with respect to these variables. Ictal recording with scalp EEG allows for differentiating between early and late remote propagation in patients with mesial temporal epilepsy and regionalized-lateralized onset seizures. Early remote propagation probably identifies a subgroup of these patients with greater uni- or bitemporal hyperexcitability.     

Intracranial EEG in temporal lobe epilepsy.

Intracranial EEG monitoring before epilepsy surgery, while becoming less commonly performed in patients with unilateral mesial temporal lobe epilepsy, is still widely used when bilateral independent temporal lobe seizures are suspected or when extratemporal foci cannot be ruled out by noninvasive means. Additionally, many epilepsy centers are reporting excellent surgical outcome in patients with neocortical temporal lobe epilepsy, when resections are guided by intracranial EEG studies. This article reviews the indications, technical aspects, risks, and interpretation of intracranial EEG in patients with temporal lobe seizures. It also considers intracranial EEG features predictive of surgical outcome.     

颅内电极记录在定位颞叶癫痫致痫灶中的应用研究

目的：通过侵袭性的术前检查(颅内电极记录)对颅内电极记录适应证进行分类，了解此方法可靠性及并发症。方法：1998～2003年间，对27例药物难治性颞叶癫痫患者进行颅内电极植人．方法包括：双侧颞叶纵向深部电极植人、双侧硬膜下颞底条状电极植人、颞外条状电极植人。结果：术前进行广泛的无创检查之后仍不能定位致痫灶的24例患者，通过颅内电极记录确定了手术。结论：对于一些难以决定是否适合手术的癫痫患者，颅内电极记录是一种有效、安全的检查方法。     

Focal ictal beta discharge on scalp EEG predicts excellent outcome of frontal lobe epilepsy surgery

PURPOSE: To determine whether a focal beta-frequency discharge at seizure onset on scalp EEG predicts outcome of frontal lobe epilepsy (FLE) surgery. METHODS: We identified 54 consecutive patients with intractable FLE who underwent epilepsy surgery between December 1987 and December 1996. A blind review of EEGs and magnetic resonance images (MRIs) was performed. Lesional epilepsy is defined as presence of an underlying structural abnormality on MRI. RESULTS: Overall, 28 (52%) patients were seizure free, with a mean follow-up of 46.5 months. Presence of a focal beta-frequency discharge at seizure onset on scalp EEG predicted seizure-free outcome in lesional (p = 0.02) and non-lesional (p = 0.01) epilepsy patients. At least 90% of patients who had either lesional or non-lesional epilepsy were seizure free if scalp EEG revealed a focal beta discharge at ictal onset. Moreover, logistic regression analysis showed that focal ictal beta pattern and completeness of lesion resection were independently predictive of seizure-free outcome. Ictal onset with lateralized EEG activity of any kind and postresection electrocorticographic spikes did not predict surgical outcome (p > 0.05). CONCLUSIONS: Only about 25% of FLE surgical patients have a focal beta-frequency discharge at seizure onset on scalp EEG. However, its presence is highly predictive of excellent postsurgical seizure control in either lesional or non-lesional FLE surgical patients.     

Hyperventilation-induced ictal fear in nonlesional temporal lobe epilepsy

Hyperventilation is a traditional seizure-provoking procedure used mainly in idiopathic generalized epilepsy and with a relatively limited role in partial epilepsy. Ictal fear is a rare seizure semiology seen in temporal lobe epilepsy. It has been suggested that the amygdala and anterior hippocampus are involved in generating ictal fear. We describe a rare patient with nonlesional temporal epilepsy who, while hyperventilating during an electroencephalography recording, developed complex partial seizures presenting as ictal fear. The particular sensitivity of the anterior hippocampus (probably the amygdala) to hypocapnia might be an important factor contributing to seizures. To avoid misdiagnosing this unusual condition as a pseudo-seizure, a detailed history and seizure semiology, as well as a concurrent electroencephalography recording, are mandatory.